*4.4. Coating Application on the Samples*

The coating procedure is illustrated in Figure 11. For a single-layer Ch coating, approximately 2 kg of flesh-cut purple sweet potatoes were dipped in 5 L of Ch solution for 2 min and dried at room temperature for 30 min. For SA gel coating, flesh-cuts were dipped in SA solution, rinsed for 30 s to remove the residual solution, and thereafter immersed in calcium chloride solution and dried. For the multilayer gel coating (ChCSA), the fresh-cuts were dipped in Ch solution for 2 min, rinsed for 30 s to remove the residual solution, immersed in calcium chloride for 2 min, then rinsed for 30 s and finally dipped in SA solution for 2 min before air-drying. Lastly, distilled water was used as an immersion solution for uncoated samples.

For each coating treatment, approximately 200 g of coated fresh-cuts were weighed and stored in triplicate in Ziploc bags (5 ◦C). Stored samples were removed at 4-days interval during a 16-day storage period and analyzed for quality parameters.

70 °C under stirring until fully dissolved to produce a 2% chitosan solution. Finally, the

The sodium alginate solution was prepared according to the method described by [11], with some modifications. Sodium alginate powder was dissolved in 100 mL of distilled water to obtain a 2% concentration. Then, the solution was stirred in a 70 °C water bath for 2 h to dissolve completely. Finally, the sodium alginate solution was cooled at

Calcium chloride was used as the cross linking agent to produce gel coatings via layer-by-layer treatment. Calcium chloride was weighed and dissolved in 100 mL of distilled water to obtain a 2% solution. Then, the solution was shaken in the incubator to

Purple flesh sweet potatoes without mechanical injuries or fungal infections were selected and washed in running water. Then, they were peeled and diced to get 1 cm

The coating procedure is illustrated in Figure 11. For a single-layer Ch coating, approximately 2 kg of flesh-cut purple sweet potatoes were dipped in 5 L of Ch solution for 2 min and dried at room temperature for 30 min. For SA gel coating, flesh-cuts were dipped in SA solution, rinsed for 30 s to remove the residual solution, and thereafter immersed in calcium chloride solution and dried. For the multilayer gel coating (ChCSA), the fresh-cuts were dipped in Ch solution for 2 min, rinsed for 30 s to remove the residual solution, immersed in calcium chloride for 2 min, then rinsed for 30 s and finally dipped in SA solution for 2 min before air-drying. Lastly, distilled water was used as an immer-

For each coating treatment, approximately 200 g of coated fresh-cuts were weighed and stored in triplicate in Ziploc bags (5 °C). Stored samples were removed at 4-days in-

pH of the solution was adjusted to 5.6 with 1 N NaOH.

room temperature.

become dissolved entirely.

pieces for flesh-cut coating.

*4.4. Coating Application on the Samples*

sion solution for uncoated samples.

*4.3. Sample Preparation*

**Figure 11.** Illustration of coating procedure for fresh-cut purple flesh sweet potatoes. **Figure 11.** Illustration of coating procedure for fresh-cut purple flesh sweet potatoes.

terval during a 16-day storage period and analyzed for quality parameters.

#### *4.5. Color Measurement 4.5. Color Measurement*

The surface color of the samples was determined by randomly selecting 3 samples and taking 3 readings for each treatment using a chromameter (CR-300, Minolta Co., Osaka, Japan). The L\*, a\*, b\* value (CIE L a b) system was numerically specified in a threedimensional spherical space defined by the three perpendicular axes: the L-axis (brightness) ranged from 0 (black) to 100% (white); the a-axis ranged from − a (green) to + a (red); The surface color of the samples was determined by randomly selecting 3 samples and taking 3 readings for each treatment using a chromameter (CR-300, Minolta Co., Osaka, Japan). The L\*, a\*, b\* value (CIE L a b) system was numerically specified in a threedimensional spherical space defined by the three perpendicular axes: the L-axis (brightness) ranged from 0 (black) to 100% (white); the a-axis ranged from − a (green) to + a (red); and the b-axis ranged from − b (blue) to + b (yellow). Total color difference (∆E) was calculated using L, a, and b values with the following equation [51]:

$$
\Delta \mathcal{E} = \sqrt{(L\_2 - L\_1)^2 + \left(a\_2 - a\_1\right)^2 + \left(b\_2 - b\_1\right)^2} \tag{1}
$$

where subscripts 1 and 2 represent the final and initial readings, respectively at a particular storage interval.
